The present invention relates to an automatic focusing unit for camera, and more particularly to an automatic focusing unit suitably adapted for use with a photographic camera on which the automatic focusing unit is detachably mounted for the purpose of automatic lens focusing on an object to be photographed.
Various automatic focusing apparatus have been developed and utilized for electrically driven cameras, particularly motion picture cameras. One currently used type of automatic focusing apparatus for a camera is the "spatial image correlation" type, examples of which are described in Isono, U.S. Pat. No. 4,093,365 and the references cited thereto. Briefly, spatial image correlation systems include two optical systems: one which is stationary and one which scans a field of view which includes the object to be photographed. Light images formed by the optical systems are distributed onto respective detector arrays of light-responsive elements. A signal is produced when the light image of the object to be photographed is similarly distributed on both detector arrays. The signal is used to control the photographic lens for automatic focusing. In such an arrangement, a scanner which scans the field of view is driven oscillatably across an angle of the field to detect the object between infinity and the minimum focus condition of the objective lens and is adjustable in response to the focus condition of the lens whereby the bisector of the scanning angle is aligned with the object, as disclosed also in Isono, U.S. Pat. No. 4,123,765.
Such an automatic focusing system is usually disposed within the camera, but recently constructed in the form of a unit separately from the camera in an attempt to produce a small-sized and economical camera. When the automatic focusing is desired, the unit is mounted on the camera. For this purpose, the automatic focusing unit is provided with a lens position detector which projects outwardly from the housing of the unit and follows the displacement of a photographic lens to obtain the positional signal of the lens and feed it back to the unit for automatic focusing. Thus, there is a possibility that the lens position detector is pushed out of a focusing ring or tube and sometimes destroyed, when it is erroneously mounted on the camera without positioning the lens position detector on a predetermined position of the focusing tube.
To overcome this drawback, a proposal has been made in which a protector for protecting the lens position detector is provided to guide the latter to a predetermined position in the mounting of the automatic focusing unit on the camera. This proposal, however, has a similar drawback because there is the possibility that the lens position detector first hits against the ring or tube and can be damaged.
To eliminate these drawbacks completely, the following conditions must be fulfilled: (1) For the detector an escapement is provided to make the detector free from an unnatural force exerted thereon when it is mounted on the camera; and (2) Means is provided to retract the detector previously to a protected area.
Therefore, it is an object of the present invention to overcome those disadvantages and provide an automatic focusing unit for a camera which can protect its lens position detector from an unnatural force exerted thereon when it is mounted on the camera.
It is another object of the present invention to provide an automatic focusing unit for a camera which can previously retract its lens position detector into a safe area in its attachment on the camera.